Procedure for producing stearyl-β-(3,5-dibutyl-4-hydroxyphenyl) propionate and bis-(β(3,5-dibutyl-4-hydroxybenzyl)-methylcarboxyethyl)sulphide

ABSTRACT

A procedure for producing stearyl-β-(3,5-dibutyl-4-hydroxyphenyl)propionate and bis-(β-(3,5-dibutyl-4-hydroxybenzyl)-methylcarboxyethyl)sulphide. In the procedure, a titanate-catalysis exchange esterification reaction is carried out with propionic acid ester conforming to formula (IV) and stearyl alcohol or thiodiglycol. ##STR1## where Bu is an n-butyl, secondary butyl, isobutyl or tertiary butyl group and R 2  is a methyl, ethyl, propyl or butyl group.

BACKGROUND OF THE INVENTION

The present invention concerns a procedure for producingstearyl-β-(3,5-dibutyl-4-hydroxyphenyl)propionate (I) andbis-(β(3,5-dibutyl-4-hydroxybenzyl)-methyl-carboxyethyl)-sulphide (II).Said products conform chemically to formulate I and II below and theyare used mainly for stabilizing substances in rubbers and plastics.##STR2## It is known in the art that these compounds can be produced ina two-step synthesis comprising (A) the addition reaction betweenalkylacrylate (III) and 2,6-dibutylphenol, and exchange esterification(B) of the product obtained (IV). ##STR3## In the procedures of priorart, step (A) is usually carried out in the presence of alkalicatalysts, either as a molten state reaction or using a solvent forfluid. The exchange esterification step (B), again, has been performedin the procedures of prior art using either alkaline or acid catalysts.

SUMMARY OF THE INVENTION

The procedure of the invention differs from procedures of prior artparticularly in that the exchange esterification step is carried outusing esters of titanic acid for a catalyst. Morever, an advantage ofthe procedure of the invention is that when said catalysts are used theexchange esterification reaction is substantially faster, and thus thereaction time shorter, than in the procedures known in the art. Anadvantage of titanate catalysts is also that the use of fluid isunnecessary and therefore the production process is simpler.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The production of the products constituting the object of the inventionmay be further simplified if the propionic acid ester (IV) is producedin a way more closely described below, because then the crude product(IV) obtained as the reaction product can be used as starting materialwithout recrystallization.

It should be noted, however, that propionic acid ester consistent withthe chemical formula (IV), whatever the procedure by which it has beenproduced, is fit to be used for starting material when step (B) iscarried out making use of the exchange esterification procedure of theinvention.

In view of the invention, it is to be recommended that the propionicacid ester (IV) is produced by an addition reaction between2,6-dibutylphenol and alkylacrylate (III) using alkali catalysts.Appropriate ones are, in that case, e.g. sodium hydroxide, potassiumhydroxide, lithium hydroxide, sodium-boron hydride, lithium-aluminiumhydride, sodium and potassium tertiary butoxide, metallic sodium andpotassium. 0.5-8% alkali catalyst, preferably 1-5%, calculated on thequantity of 2,6-dibutylphenol, are used.

It is possible in view of the invention that the step (A) is performedeither as a molten state reaction or using a solvent for fluid. Solventswhich are appropriate are then e.g. dimethylformamide, dimethylacetamideor dimethylsulphoxide, hexamethylphosphamide, acetonitrile,propionitrile or sulphonitrile, sulpholan, dimethylene glycol,tetrahydrofurane or tertiary butylalcohol. Of these, particularlytertiary butylalcohol is well suited to be used in the procedure of theinvention. An appropriate quantity of the solvent is 5 parts by weightor less, preferably 0.1-1 parts by weight, of the quantity of2,6-dibutylphenol.

It is recommendable in view of the invention that the molar proportionof alkylacrylate and 2,6-dibutylphenol in the addition step (A) is inthe range 0.7-1.3, preferably 0.8-1.1, the reaction temperature is60°-130° C., preferably 70°-100° C., and the reaction time is 2-12 h,preferably 6-8 h. All conventional mixing reactors are appropriate foraccomplishing the reaction. It is furthermore recommendable in view ofthe procedure that it can be carried out in a nitrogen atmosphere.Propionic acid ester (IV) thus produced is sufficiently pure to be usedas starting material for the purposes of the invention. However, thefurther use requires that the alkali catalyst is neutralized e.g. withthe aid of carboxylic acids or mineral acids and that low-boilingimpurities are separated by distilling. The propionic acid ester maythen be used in the transesterification reaction without additionalpurification.

In the procedure of the invention, the exchange esterification step isaccomplished using for a catalyst titanic acid esters, particularlytetraalkyl orthotitanates, such as methylethyl, tetramethyl, tetraethyl,n-propyl or isopropyl, n-butyl or isobutyl orthotitanate, orn-butyltitanate polymers. Particularly recommendable in view of theinvention is the use as catalyst of tetra-n-butyltitanate. Therecommendable quantity of titanate catalyst is 0.1-5%, preferably0.5-0.3%, of the quantity of propionic acid ester.

In the procedure of the invention, the exchange esterification may becarried out in a fluid or directly in the melt. It is more recommendedto carry out the reaction in the melt because hereby the use of extrasolvent is avoided and the process is simplified.

When the procedure of the invention is used it is advisable that in theexchange esterification step the molar proportion between propionic acidester and stearyl alcohol is 0.8-1.5, preferably 0.9-1.2, respectively,the molar proportion between propionic acid ester and thiodiglycol is1.6-3.0, preferably 1.8-2.2. The recommended reaction temperature is60°-180° C., preferably 60°-160° C., more preferably 80°-130° C., mostpreferably 90°-130° C., and the reaction time 1-10 h, preferably 2-6 h.Moreover, it is advisable that during the reaction the low-boilingalcohol which is released in the exchange esterification is removed. Inpractice, this can be implemented by accomplishing the reaction e.g. at2-20 mmHg vacuum.

The purification of the products of the invention can be accomplishede.g. by fraction crystallization. Suitable solvents are then hexane,cyclohexane, heptane, ethanol, ispropanol, n-butanol, isobutanol andsecondary butanol. Particularly well suited solvents are propylalcoholor butylalcohol either alone or together with a small quantity of water.

The procedure of the invention thus differs from the procedure known inthe art in that in the exchange esterification step esters of titanicacid have been used for the catalyst. Hereby, the exchangeesterification can be accomplished in considerably shorter time, up toone half of the time required when acid or alkali catalysts of prior artare used. Moreover, less of the coloured impurities are now formed. Aconsiderable advantage of the new catalyst is also that the exchangeesterification reaction can with ease be accomplished directly in themelt, without extra solvent fluid, and this makes the process simplerand more economic. If, moreover, the propionic acid ester used in theexchange esterification as starting material is produced in the mannerdescribed in the foregoing, the production process is furthersimplified, since in that case purification of the intermediate productis not absolutely necessary.

In the following, the procedure of the invention is described more indetail with the aid of the following examples.

EXAMPLE 1 Production of3,5-di-tertiary-butyl-4-hydroxphenyl-methylpropionate

52 ml tertiary butanol, 2.84 g potassium tertiary butoxide, 186.5 g2,6-di-tertiary butylphenol and 78.0 g methylacrylate were added in areactor provided with mixing, refluxing system and N₂ flushing. Thestarting materials were allowed to react at 85°-90° C. in an N₂atmosphere, with continuous agitation of the mixture. The product wasneutralized with 1.7 ml acetic acid and, finally, vacuum was produced inthe equipment for removing the low-boiling impurities. The obtainedsample was used as starting material in the exchange esterification stepeither as such or it was purified by recrystallizing from 95-%isopropanol; yield 206 g (70%), m.p. 64° C.

EXAMPLE 2 Production of stearyl-β(3,5-dibutyl-4-hydroxphenyl)propionate

5.4 g octadecanol and 6.0 g of the propionic acid ester produced inExample 1 were heated in vacuum at 100° C./50 mmHg for removingmoisture, if any, and low-boiling impurities. Thereafter, 0.1 mltetrabutyltitanate were added for catalyst, and the starting materialswere allowed to react for 3 h at 95° C./5 mmHg so that the liberatedmethanol was distilled off during the reaction. 0.05 mltetrabutyltitanate were added and the reaction was continued another 30min. The mixture was dissolved in isopropanol, to which 0.5 ml water wasadded to decompose the catalyst; yield 8.5 g (80%), m.p. 46°-48° C. Theproduct was recrystallized from 90% isopropanol, m.p. 50°-52° C.

EXAMPLE 3 Production of stearyl-β(3,5-dibutyl-4-hydroxphenyl)propionate

5.4 g octadecanol and 5.9 g propionic acid ester produced in Example 1,with 0.05 ml tetrabutyltitanate for catalyst, were allowed to react at105°-110° C./5 mmHg for 2 hrs. The product was recrystallized from 90%isopropanol; yield 8.7 g (82%), m.p. 50°-52° C.

EXAMPLE 4 Production ofbis-(β-3,5-dibutyl-4-hydroxybenzyl)-methylcarboxyethyl)sulphide

1.22 g thiodiglycol and 5.9 g propionic acid ester produced in Example 1were heated at 80°-90° C./7 mmHg for 30 min for removing the moisture,if any, and low-boiling impurities. 0.1 ml tetrabutyltitanate was addedas catalyst, and the starting materials were allowed to react for 1 hourat 100° C./7 mmHg so that the methanol that was formed was distilledoff. 0.1 ml tetrabutyltitanate were added, and reaction was allowed toreact during 3 hrs at 120° C./7 mmHg. 0.35 g thiodiglycol were added,and the reaction was continued for another 30 min. The product waspurified by crystallizing it from 90% isopropanol; yield 5.1 g (79%),m.p. 68°-75° C.

EXAMPLE 5 Produciton ofbis-(β-(3,5-dibutyl-4-hydroxybenzyl)-methylcarboxyethyl)sulphide

1.3 g thiodiglycol and 5.84 g propionic acid ester produced as inExample 1 were allowed to react in the presence of tetrabutyltitanate(0.05 ml) as catalyst, at 100° C./8 mmHg during 1 h, and further at120°-130° C./8 mmHg for 1 h. 0.6 ml thiodiglycol and 0.05 mltetrabutyltitanate were added, and the reaction was continued at 120°C./10 mmHg for 1.5 h. The excess thiodiglycol was distilled off and theproduct was crystallized from 90% isopropanol; yield 3.3 g (51%), m.p.68°-75° C.

We claim:
 1. Method for producingstearyl-β-(3,5-dibutyl-4-hydroxyphenyl)propionate orbis-(β-3,5-dibutyl-4-hydroxy-benzyl)methylcarboxethyl)sulphide,bytransesterification of a propionic acid ester of the formula ##STR4##wherein Bu is an n-, secondary, iso- or tertiary butyl group and R₂ isan alkyl group containing 1 to 4 carbon atoms, which comprises reactingsaid propionic acid ester with a stearyl alcohol or thiodiglycol in thepresence of a transesterification catalytic effective amount of atitanic acid ester as catalyst in the transesterification, whereby thetransesterification reaction is accelerated to form the correspondingpropionate or sulphide.
 2. The method of claim 1, comprisingreacting amolar proportion of said propionic acid ester: said stearyl alcoholabout 0.9-1.2, or reacting a molar proportion of said propionic acidester: said thiodiglycol of about 1.0-2.0.
 3. The method of claim 1,comprisingcarrying out the reaction in the presence of a quantity ofsaid titanic acid ester as catalyst which is about 0.1-5% of a quantityof said propionic acid ester.
 4. The method of claim 1, wherein saidtitanic acid ester is tetra-alkyl orthotitanate.
 5. The method of claim4, wherein said tetra-alkyl orthotitanate is isopropyl or n-butyltitanate.
 6. The method of claim 1, wherein the reaction is carried outat a temperature of about 60°-160° C.
 7. The method of claim 1, whereinthe reaction is carried out over a time of about 1-10 hours.
 8. Themethod of claim 1, wherein said reaction is carried out in a fluidmedium, or in the form of a melt without fluid.
 9. The method of claim1, additionally comprisingreacting an alkyl acrylate of the formula##STR5## wherein R₂ is an alkyl group containing 1 to 4 carbon atomswith 2,6-dibutylphenol in the presence of an alkali catalyst to producesaid propionic acid ester, distilling off low boiling impurities andneutralizing said alkali catalyst with of carboxylic acid or mineralacid, and then utilizing said propionic acid ester in saidtransesterification reaction without additional purification.
 10. Themethod of claim 9, comprisingcarrying out the reaction for producingsaid propionic acid ester in the presence of a quantity of said alkalicatalyst which is about 1-5% of a quantity of said 2,6-dibutylphenol.11. The method of claim 10, comprisingreacting a molar proportion ofsaid alkyl acrylate: said 2,6-dibutylphenol of about 0.7-1.3.
 12. Themethod of claim 9, wherein the reaction for producing said propionicacid ester is carried out at a temperature of about 70°-100° C. and overa time of about 2-12 hours.